Original asus firmware for RT-N16 allowed to "mirror" a LAN port to a WAN interface, so that if a device is plugged in to port 4, or 1 of the LAN, it would be bridged with the WAN port and act independently of the rest of the network devices that are NAT'ted.
This is very useful when an IPTV appliance is installed, 'cause they are damn sensitive to NAT, and ISP recommends to set them up so that they are not "behind" the router.

Such option in GUI would be very beneficial for IPTV users and appreciated.